US11796677B2 - Optical sensor system - Google Patents

Abstract

A LIDAR system includes a LIDAR chip and local electronics that receive signals from the LIDAR chip. The local electronics are configured to operate one or more components on the LIDAR chip such that the LIDAR chip transmits an optical data signal from the LIDAR chip such that optical data signal includes data generated from the signals received from the LIDAR chip.

Description

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/697,266, filed on Jul. 12, 2018, entitled “Optical Sensor System,” and incorporated herein in its entirety.

FIELD

The invention relates to optical devices. In particular, the invention relates to LIDAR chips.

BACKGROUND

There is an increasing commercial demand for 3D sensing systems that can be economically deployed in applications such as ADAS (Advanced Driver Assistance Systems) and AR (Augmented Reality). LIDAR (Light Detection and Ranging) sensors are used to construct a 3D image of a target scene by illuminating the scene with laser light and measuring the returned signal.

Frequency Modulated Continuous Wave (FMCW) is an example of a coherent detection method that can be used for LIDAR applications. The FMCW technique is capable of determining the distance and/or radial velocity between an object and a source of a LIDAR output signal. Additionally, FMCW techniques have reduced sensitivity to ambient light and light from other LIDAR systems.

An integrated FMCW LIDAR chip is not yet available. Additionally, efforts to generate chips that have a portion of the LIDAR chip components have been limited in the amount of optical power they can transmit without signal degradation. This signal degradation limits the amount of transmitted laser power to the reflecting object. This limit to the amount of transmitted laser power limits overall sensitivity of the device. For these reasons, there is a need for a platform capable of integrating the LIDAR chip.

SUMMARY

A LIDAR chip includes a utility waveguide that carries an outgoing LIDAR signal to a facet through which the outgoing LIDAR signal exits from the chip. An optical component combines a first portion of a reference signal with a first portion of a comparative signal. The reference signal includes a portion of the light from the outgoing LIDAR signal before the outgoing LIDAR signal exits from the chip and the comparative signal includes light reflected off an object located off the chip. The chip includes second optical component that combines a second portion of the reference signal with a second portion of the comparative signal, the second portion of the reference signal being phase shifted relative to the first portion of the reference signal. In some instances, the phase shift is ninety degrees.

A LIDAR system includes electronics in electrical communication with a LIDAR chip. The electronics receive multiple data electrical signals from a LIDAR chip and perform a Complex Fourier transform on a complex signal. One of the data electrical signals is a real component of the complex signal and another one of the data electrical signals is an imaginary component of the complex signal.

A method of identifying the radial velocity and/or distance between a reflecting object and source of a LIDAR output signal includes generating multiple data electrical signals and performing a Complex Fourier transform on a complex signal where one of the data electrical signals is a real component of the complex signal and another one of the data electrical signals is an imaginary component of the complex signal.

The LIDAR system has a LIDAR chip that includes an optical port through which a light signal exits from the optical chip. The light signal includes light reflected from an object off the chip.

Another embodiment of a LIDAR system includes a LIDAR chip and local electronics that receive signals from the LIDAR chip. The local electronics are configured to operate one or more components on the LIDAR chip so as to transmit an optical data signal from the LIDAR chip such that optical data signal includes data generated from the signals received from the LIDAR chip.

BRIEF DESCRIPTION OF THE FIGURES

FIG.1 is a top view of a LIDAR chip.

FIG.2 is a cross-section of a LIDAR chip according toFIG.1 constructed from a silicon-on-insulator wafer.

FIG.3 illustrates the LIDAR chip ofFIG.1 used with an off-chip scanning mechanism.

FIG.4 illustrates the LIDAR chip ofFIG.1 used with another embodiment of an off-chip scanning mechanism.

FIG.5 is a cross section of the LIDAR chip ofFIG.1 having an integrated scanning mechanism.

FIG.6A illustrates the chip ofFIG.1 modified to include multiple different balanced detectors for further refining data generated by the chip.

FIG.6B provides a schematic of electronics that are suitable for use with the chip ofFIG.6A.

FIG.6C is a graph of magnitude versus frequency. A solid line on the graph shows results for a Complex Fourier transform performed on output generated from the LIDAR chip ofFIG.6B.

FIG.7 is a diagram of a vehicle that includes aheadlight150 and atrunk152. The car includes a LIDARmodule154 located near theheadlight150.

FIG.8 illustrates a LIDAR system where electronics are distributed among remote electronics and local electronics.

FIG.9 illustrates an embodiment of a LIDAR system where optical components are distributed among remote electronics and a LIDAR chip.

FIG.10 illustrates the LIDAR chip ofFIG.1 modified to include a data processing branch for generation and transmission of an optical data signal that is transmitted from the LIDAR chip to remote electronics on a communications link.

FIG.11 illustrates the LIDAR chip ofFIG.6A throughFIG.6C modified to include a data processing branch.

FIG.12A includes a LIDAR chip with multiple data light source that are each the source of a different outgoing data signal on a data waveguide.

FIG.12B illustrates the LIDAR chip ofFIG.10 modified to generate multiple different optical data signals.

FIG.13 illustrates an example of the distribution of the electronics functionality between local electronics and the remote electronics.

DESCRIPTION

A LIDAR chip is disclosed that includes LIDAR branch and one or more data processing branches. The LIDAR branch includes optical components for generating optical LIDAR signals that carry LIDAR data such as the distance and/or radial velocity between the LIDAR chip and a reflecting object located off the LIDAR chip. The one or more data processing branches include components for generating optical data signals that are used to transmit data to remote electronics. The data included in the optical data signals can include LIDAR data and/or other data.

The LIDAR chip is associated with local electronics. The local electronics can operate the LIDAR chip so as to generate the LIDAR signals. In some instances, the local electronics process the LIDAR signals and/or electrical signals generated from the LIDAR signals so as to generate the LIDAR data and encode the LIDAR data onto the optical data signals. The LIDAR chip can transmit the optical data signals to remote electronics. As a result, the one or more data processing branches provide a mechanism for communicating data from and/or about the LIDAR branch to remote electronics. The LIDAR branch and one or more data processing branches are disclosed using components that are suitable for construction on a variety of platforms such as the silicon-on-insulator (SOI) platform. Accordingly, an integrated LIDAR chip is disclosed.

FIG.1 is a topview of a LIDAR chip that includes a laser cavity. The laser cavity includes alight source10 that can include or consist of a gain medium (not shown) for a laser. The chip also includes acavity waveguide12 that receives a light signal from thelight source10. The light source can be positioned in arecess13 so a facet of the light source is optically aligned with a facet of thecavity waveguide12 to allow the light source andcavity waveguide12 to exchange light signals. Thecavity waveguide12 carries the light signal to apartial return device14. The illustratedpartial return device14 is an optical grating such as a Bragg grating. However, otherpartial return devices14 can be used; for instance, mirrors can be used in conjunction with echelle gratings and arrayed waveguide gratings.

Thepartial return device14 returns a return portion of the light signal to thecavity waveguide12 as a return signal. For instance, thecavity waveguide12 returns the return signal to thelight source10 such that the return portion of the light signal travels through the gain medium. Thelight source10 is configured such that at least a portion of the return signal is added to the light signal that is received at thecavity waveguide12. For instance, thelight source10 can include a highly, fully, or partiallyreflective device15 that reflects the return signal received from the gain medium back into the gain medium. As a result, light can resonate between thepartial return device14 and thereflective device15 so as to form a laser cavity such as a Distributed Bragg Reflector (DBR) laser cavity. A DBR laser cavity has an inherently narrow-linewidth and a longer coherence length than DFB lasers and accordingly improves performance when an object reflecting the LIDAR output signal from the chip is located further away from the chip.

Thepartial return device14 passes a portion of the light signal received from thecavity waveguide12 to autility waveguide16 included on the chip. The portion of the light signal that theutility waveguide16 receives from thepartial return device14 serves as the output of the laser cavity. The output of the laser cavity serves as an outgoing LIDAR signal on theutility waveguide16. Theutility waveguide16 terminates at afacet18 and carries the outgoing LIDAR signal to thefacet18. Thefacet18 can be positioned such that the outgoing LIDAR signal traveling through thefacet18 exits the chip and serves as a LIDAR output signal. For instance, thefacet18 can be positioned at an edge of the chip so the outgoing LIDAR signal traveling through thefacet18 exits the chip and serves as a LIDAR output signal.

The LIDAR output signal travels away from the chip and is reflected by objects in the path of the LIDAR signal. The reflected signal travels away from the objects. At least a portion of the reflected signal returns to thefacet18 of theutility waveguide16. Accordingly, a portion of the reflected signal can enter theutility waveguide16 through thefacet18 and serve as a LIDAR input signal guided by theutility waveguide16.

Theutility waveguide16 can include a tapered portion before thefacet18. For instance, theutility waveguide16 can include ataper20 that terminate at thefacet18. Thetaper20 can relax the alignment tolerances required for efficient coupling of theutility waveguide16 to the LIDAR input light and the outgoing LIDAR signal. Accordingly, thetaper20 can increase the percentage of the LIDAR input signal that is successfully returned to the chip for processing. In some instances, thetaper20 is constructed such that thefacet18 has an area that is more than two, five, or ten times the area of a cross section of a straight portion of theutility waveguide16. AlthoughFIG.1 shows thetaper20 as a horizontal taper, thetaper20 can be a horizontal and/or vertical taper. The horizontal and/or vertical taper can be linear and/or curved. In some instances, thetaper20 is an adiabatic taper.

The chip includes adata branch24 where the optical signals that are processed for LIDAR data are generated. The data branch includes anoptical coupler26 that moves a portion of the light signals from theutility waveguide16 into the data branch. For instance, anoptical coupler26 couples a portion of the outgoing LIDAR signal from theutility waveguide16 onto areference waveguide27 as a reference signal. Thereference waveguide27 carries the reference signal to a light-combiningcomponent28.

Theoptical coupler26 also couples a portion of the LIDAR input signal from theutility waveguide16 onto acomparative waveguide30 as a comparative signal. The comparative signal includes at least a portion of the light from the LIDAR input signal. The comparative signal can exclude light from the reference light signal. Thecomparative waveguide30 carries the comparative signal to the light-combiningcomponent28.

The illustratedoptical coupler26 is a result of positioning theutility waveguide16 sufficiently close to thereference waveguide27 and thecomparative waveguide30 that light from theutility waveguide16 is coupled into thereference waveguide27 and thecomparative waveguide30; however, other signal tapping components can be used to move a portion of the of the light signals from theutility waveguide16 onto thereference waveguide27 and thecomparative waveguide30. Examples of suitable signal tapping components include, but are not limited to, y-junctions, multi-mode interference couplers (MMIs), and integrated optical circulators.

The light-combiningcomponent28 combines the comparative signal and the reference signal into a composite signal. The reference signal includes light from the outgoing LIDAR signal. For instance, the reference signal can serve as a sample of the outgoing LIDAR signal. The reference signal can exclude light from the LIDAR output signal and the LIDAR input signal. In contrast, the comparative signal light includes light from the LIDAR input signal. For instance, the comparative signal can serve as a sample of the LIDAR input signal. Accordingly, the comparative signal has been reflected by an object located off the chip while the LIDAR output signal has not been reflected. When the chip and the reflecting object are moving relative to one another, the comparative signal and the reference signal have different frequencies due to the Doppler effect. As a result, beating occurs between the comparative signal and the reference signal.

The light-combiningcomponent28 also splits the resulting composite sample signal onto afirst detector waveguide36 and asecond detector waveguide38. Thefirst detector waveguide36 carries a first portion of the composite sample signal to afirst light sensor40 that converts the first portion of the composite sample signal to a first electrical signal. Thesecond detector waveguide38 carries a second portion of the composite sample signal to a secondlight sensor42 that converts the second portion of the composite sample signal to a second electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

Thelight combining component28, thefirst light sensor40 and the secondlight sensor42 can be connected as a balanced photodetector that outputs an electrical data signal. For instance, thelight combining component28, thefirst light sensor40 and the secondlight sensor42 can be connected such that the DC components of the signal photocurrents cancel, improving detection sensitivity. Suitable methods for connecting thefirst light sensor40 and the secondlight sensor42 as balanced photodetectors includes connecting thefirst light sensor40 and the secondlight sensor42 in series. In one example, thefirst light sensor40 and the secondlight sensor42 are both avalanche photodiodes connected in series. Balanced photodetection is desirable for detection of small signal fluctuations.

An example of a suitable light-combiningcomponent28 is a Multi-Mode Interference (MMI) device such as a 2×2 MMI device. Other suitable light-combiningcomponents28 include, but are not limited to, adiabatic splitters, and directional coupler. In some instances, the functions of the illustrated light-combiningcomponent28 are performed by more than one optical component or a combination of optical components.

A single light sensor can replace thefirst light sensor40 and the secondlight sensor42 and can output the data signal. When a single light sensor replaces thefirst light sensor40 and the secondlight sensor42, the light-combiningcomponent28 need not include light-splitting functionality. As a result, the illustrated light light-combiningcomponent28 can be a 2×1 light-combining component rather than the illustrated 2×1 light-combining component. For instance, the illustrated light light-combining component can be a 2×1 MMI device. In these instances, the chip includes a single detector waveguide that carries the composite sample signal to the light sensor.

The data branch includes a dataoptical attenuator44 positioned along thecomparative waveguide30 such that the dataoptical attenuator44 can be operated so as to attenuate the comparative signal on thecomparative waveguide30. The chip also includes an outputoptical attenuator46 positioned along theutility waveguide16 such that the outputoptical attenuator46 can be operated so as to attenuate the outgoing LIDAR signal on theutility waveguide16. Suitable attenuators for the dataoptical attenuator44 and/or the outputoptical attenuator46 are configured to attenuate intensity of a light signal. Examples of a suitable attenuator configured to attenuate intensity of a light signal include carrier injection based PIN diodes, electro-absorption modulators, and Mach-Zehnder (MZ) modulators.

The chip also includes a samplingdirectional coupler50 that couples a portion of the comparative signal from thecomparative waveguide30 onto asampling waveguide52. The coupled portion of the comparative signal serves as a sampling signal. Thesampling waveguide52 carries the sampling signal to asampling light sensor54. AlthoughFIG.1 illustrates a samplingdirectional coupler50 moving a portion of the comparative signal onto thesampling waveguide52, other signal tapping components can be used to move a portion of the comparative signal from thecomparative waveguide30 onto thesampling waveguide52. Examples of suitable signal tapping components include, but are not limited to, y-junctions, and MMIs.

The chip includes acontrol branch55 for controlling operation of the laser cavity. The control branch includes adirectional coupler56 that moves a portion of the outgoing LIDAR signal from theutility waveguide16 onto acontrol waveguide57. The coupled portion of the outgoing LIDAR signal serves as a tapped signal. AlthoughFIG.1 illustrates adirectional coupler56 moving portion of the outgoing LIDAR signal onto thecontrol waveguide57, other signal-tapping components can be used to move a portion of the outgoing LIDAR signal from theutility waveguide16 onto thecontrol waveguide57. Examples of suitable signal tapping components include, but are not limited to, y-junctions, and MMIs.

Thecontrol waveguide57 carries the tapped signal to aninterferometer58 that splits the tapped signal and then re-combines the different portions of the tapped signal with a phase differential between the portions of the tapped signal. The illustratedinterferometer58 is a Mach-Zehnder interferometer; however, other interferometers can be used.

Theinterferometer58 outputs a control light signal on aninterferometer waveguide60. Theinterferometer waveguide60 carries the control light signal to acontrol light sensor61 that converts the control light signal to an electrical signal that serves as an electrical control signal. The interferometer signal has an intensity that is a function of the frequency of the outgoing LIDAR signal. For instance, a Mach-Zehnder interferometer will output a sinusoidal control light signal with a fringe pattern. Changes to the frequency of the outgoing lidar signal will cause changes to the frequency of the control light signal. Accordingly, the frequency of the electrical control signal output from thecontrol light sensor61 is a function of the frequency of the outgoing lidar signal. Other detection mechanisms can be used in place of thecontrol light sensor61. For instance, thecontrol light sensor61 can be replaced with a balanced photodetector arranged as thelight combining component28, thefirst light sensor40 and the secondlight sensor42.

Electronics62 can operate one or more components on the chip. For instance, theelectronics62 can be in electrical communication with and control operation of thelight source10, the dataoptical attenuator44, outputoptical attenuator46, thefirst light sensor40, the secondlight sensor42, the samplinglight sensor54, and thecontrol light sensor61. Although theelectronics62 are shown off the chip, all or a portion of the electronics can be included on the chip. For instance, the chip can include electrical conductors that connect thefirst light sensor40 in series with the secondlight sensor42.

Theelectronics62 can include asource control module63. During operation of the chip, thesource control module63 can operate thelight source10 such that the laser cavity outputs the outgoing LIDAR signal. Thesource control module63 can operate the light source through a series of cycles where each cycle generates at least a distance data point. During each cycle, the data signal is sampled multiple times. During each of the samples, thesource control module63 tune the frequency of the outgoing LIDAR signal. As will be described in more detail below, thesource control module63 can employ output from the control branch in order to control the frequency of the outgoing LIDAR signal such that the frequency of the outgoing LIDAR signal as a function of time is known to the electronics. In some instance, a cycle includes a first sample and a second sample. During the first sample, thesource control module63 can increase the frequency of the outgoing LIDAR signal and during a second sample thesource control module63 can decrease the frequency of the outgoing LIDAR signal. For instance, the laser cavity can be configured to output an outgoing LIDAR signal (and accordingly a LIDAR output signal) with a wavelength of 1550 nm. During the first sample, thesource control module63 can increase the frequency of the outgoing LIDAR signal (and accordingly a LIDAR output signal) such that the wavelength decreases from 1550 nm to 1459.98 nm followed by decreasing the frequency of the outgoing LIDAR signal such that the wavelength increases from 1459.98 nm to 1550 nm.

When the outgoing LIDAR signal frequency is increased during the first sample, the LIDAR output signal travels away from the chip and then returns to the chip as a LIDAR input signal. A portion of the LIDAR input signal becomes the comparative signal. During the time that the LIDAR output signal and the LIDAR input signal are traveling between the chip and a reflecting object, the frequency of the outgoing LIDAR signal continues to increase. Since a portion of the outgoing LIDAR signal becomes the reference signal, the frequency of the reference signal continues to increase. As a result, the comparative signal enters the light-combining component with a lower frequency than the reference signal concurrently entering the light-combining component. Additionally, the further the reflecting object is located from the chip, the more the frequency of the reference signal increases before the LIDAR input signal returns to the chip. Accordingly, the larger the difference between the frequency of the comparative signal and the frequency of the reference signal, the further the reflecting object is from the chip. As a result, the difference between the frequency of the comparative signal and the frequency of the reference signal is a function of the distance between the chip and the reflecting object.

For the same reasons, when the outgoing LIDAR signal frequency is decreased during the second sample, the comparative signal enters the light-combining component with a higher frequency than the reference signal concurrently entering the light-combining component and the difference between the frequency of the comparative signal and the frequency of the reference signal during the second sample is also function of the distance between the chip and the reflecting object.

In some instances, the difference between the frequency of the comparative signal and the frequency of the reference signal can also be a function of the Doppler effect because relative movement of the chip and reflecting object can also affect the frequency of the comparative signal. For instance, when the chip is moving toward or away from the reflecting object and/or the reflecting object is moving toward or away from the chip, the Doppler effect can affect the frequency of the comparative signal. Since the frequency of the comparative signal is a function of the radial velocity between the reflecting object and the LIDAR chip, the difference between the frequency of the comparative signal and the frequency of the reference signal is also a function of the speed the reflecting object is moving toward or away from the chip and/or the speed the chip is moving toward or away from the reflecting object. Accordingly, the difference between the frequency of the comparative signal and the frequency of the reference signal is a function of the distance between the chip and the reflecting object and is also a function of the Doppler effect.

The composite sample signal and the data signal each effectively compares the comparative signal and the reference signal. For instance, since the light-combining component combines the comparative signal and the reference signal and these signals have different frequencies, there is beating between the comparative signal and reference signal. Accordingly, the composite sample signal and the data signal have a beat frequency related to the frequency difference between the comparative signal and the reference signal and the beat frequency can be used to determine the difference in the frequency of the comparative signal and the reference signal. A higher beat frequency for the composite sample signal and/or the data signal indicates a higher differential between the frequencies of the comparative signal and the reference signal. As a result, the beat frequency of the data signal is a function of the distance between the chip and the reflecting object and is also a function of the Doppler effect.

Theelectronics62 can include adata module64 that can use the composite sample signal and the data signal to determine the distance between the chip and the reflecting object and/or the radial velocity of the chip and the reflecting object (i.e., the contribution of the Doppler effect). As noted above, the beat frequency is a function of two unknowns; the distance between the chip and the reflecting object and the radial velocity of the chip and the reflecting object (i.e., the contribution of the Doppler effect). The use of multiple different samples permits thedata module64 to resolve the two unknowns. For instance, the beat frequency determined for the first sample is related to the unknown distance and Doppler contribution and the beat frequency determined for the second sample is also related to the unknown distance and Doppler contribution. The availability of the two relationships allows thedata module64 to resolve the two unknowns. Accordingly, the distance between the chip and the reflecting object can be determined without influence from the Doppler effect. Further, in some instances, thedata module64 use this distance in combination with the Doppler effect to determine the radial velocity of the reflecting object toward or away from the chip.

In instances where the radial velocity of target and source is zero or very small, the contribution of the Doppler effect to the beat frequency is essentially zero. In these instances, the Doppler effect does not make a substantial contribution to the beat frequency and theelectronics62 can take only the first sample to determine the distance between the chip and the reflecting object.

During operation, thesource control module63 can adjust the frequency of the outgoing LIDAR signal in response to the electrical control signal output from thecontrol light sensor61. As noted above, the magnitude of the electrical control signal output from thecontrol light sensor61 is a function of the frequency of the outgoing LIDAR signal. Accordingly, thesource control module63 can adjust the frequency of the outgoing LIDAR signal in response to the magnitude of the electrical control signal. For instance, while changing the frequency of the outgoing LIDAR signal during one of the samples, theelectronics62 can have a range of suitable values for the electrical control signal magnitude as a function of time. At multiple different times during a sample, thesource control module63 can compare the electrical control signal magnitude to the range of values associated with the current time in the sample. If the electrical control signal magnitude indicates that the frequency of the outgoing LIDAR signal is outside the associated range of electrical control signal magnitudes, thesource control module63 can operate thelight source10 so as to change the frequency of the outgoing LIDAR signal so it falls within the associated range. If the electrical control signal magnitude indicates that the frequency of the outgoing LIDAR signal is within the associated range of electrical control signal magnitudes, thesource control module63 does not change the frequency of the outgoing LIDAR signal.

Theelectronics62 can include apower module65 configured to operate the outputoptical attenuator46. During operation, thepower module65 can adjust the level of attenuation provided by the outputoptical attenuator46 in response to the sampling signal from the samplinglight sensor54. For instance, thepower module65 can operate the outputoptical attenuator46 so as to increase the level of attenuation in response to the magnitude of the sampling signal being above a first signal threshold and/or decrease the magnitude of the power drop in response to the magnitude of the sampling signal being below a second signal threshold.

In some instance, thepower module65 adjusts the level of attenuation provided by the outputoptical attenuator46 to prevent or reduce the effects of back-reflection on the performance of the laser cavity. For instance, the first signal threshold and/or the second signal threshold can optionally be selected to prevent or reduce the effects of back-reflection on the performance of the laser cavity. Back reflection occurs when a portion of the LIDAR input signal returns to the laser cavity as a returned LIDAR signal. In some instances, on the order of 50% of the LIDAR input signal that passes through thefacet18 returns to the laser cavity. The returned LIDAR signal can affect performance of the laser cavity when the power of the returned LIDAR signal entering thepartial return device14 does not decrease below the power of the outgoing LIDAR signal exiting from the partial return device14 (“power drop”) by more than a minimum power drop threshold. In the illustrated chip, the minimum power drop threshold can be around 35 dB (0.03%). Accordingly, the returned lidar signal can affect the performance of the laser cavity when the power of the returned LIDAR signal entering thepartial return device14 is not more than 35 dB below the power of the outgoing LIDAR signal exiting from thepartial return device14.

Thepower module65 can operate the outputoptical attenuator46 so as to reduce the effect of low power drops, e.g. when the target object is very close or highly reflective or both. As is evident fromFIG.1, operation of the outputoptical attenuator46 so as to increase the level of attenuation reduces the power of the returned LIDAR signal entering thepartial return device14 and also reduces the power of the returned outgoing LIDAR signal at a location away from thepartial return device14. Since the outputoptical attenuator46 is located apart from thepartial return device14, the power of the outgoing LIDAR signal exiting from thepartial return device14 is not directly affected by the operation of the outputoptical attenuator46. Accordingly, the operation of the outputoptical attenuator46 so as to increase the level of attenuation increases the level of the power drop. As a result, the electronics can employ theoptical attenuator46 so as to tune the power drop.

Additionally, the magnitude of the sampling signal is related to the power drop. For instance, the magnitude of the sampling signal is related to the power of the comparative signal as is evident fromFIG.1. Since the comparative signal is a portion of the lidar input signal, the magnitude of the sampling signal is related to the power of the lidar input signal. This result means the magnitude of the sampling signal is also related to the power of the returned LIDAR signal because the returned LIDAR signal is a portion of the lidar input signal. Accordingly, the magnitude of the sampling signal is related to the power drop.

Since the magnitude of the sampling signal is related to the power drop, thepower module65 can use the magnitude of the sampling signal to operate the output optical attenuator so as to keep the magnitude of the comparative signal power within a target range. For instance, thepower module65 can operate the outputoptical attenuator46 so as to increase the magnitude of the power drop in response to the sampling signal indicating that the magnitude of power drop is at or below a first threshold and/or theelectronics62 can operate the outputoptical attenuator46 so as to decrease the magnitude of the power drop in response to the sampling signal indicating that the magnitude of power drop is at or above a second threshold. In some instances, the first threshold is greater than or equal to the minimum power drop threshold. In one example, thepower module65 operates the outputoptical attenuator46 so as to increase the magnitude of the power drop in response to the magnitude of the sampling signal being above a first signal threshold and/or decrease the magnitude of the power drop in response to the magnitude of the sampling signal being below a second signal threshold. The identification of the value(s) for one, two, three, or four variables selected from the group consisting of the first threshold, the second threshold, the first signal threshold, and the second signal threshold can be determined from calibration of the optical chip during set-up of the LIDAR chip system.

Theelectronics62 can include adata control module66 configured to operate the dataoptical attenuator44. Light sensors can become saturated when the power of the composite light signal exceeds a power threshold. When a light sensor becomes saturated, the magnitude of the data signal hits a maximum value that does not increase despite additional increases in the power of the composite light signal above the power threshold. Accordingly, data can be lost when the power of the composite light signal exceeds a power threshold. During operation, thedata control module66 can adjust the level of attenuation provided by the dataoptical attenuator44 so the power of the composite light signal is maintained below a power threshold.

As is evident fromFIG.1, the magnitude of the sampling signal is related to the power of the comparative signal. Accordingly, thedata control module66 can operate the dataoptical attenuator44 in response to output from the sampling signal. For instance, thedata control module66 can operate the data optical attenuator so as to increase attenuation of the comparative signal when the magnitude of the sampling signal indicates the power of the comparative signal is above an upper comparative signal threshold and/or can operate the data optical attenuator so as to decrease attenuation of the comparative signal when the magnitude of the sampling signal indicates the power of the comparative signal is below a lower comparative signal threshold. For instance, in some instances, thedata control module66 can increase attenuation of the comparative signal when the magnitude of the sampling signal is at or above an upper comparative threshold and/or thedata control module66 decrease attenuation of the comparative signal when the magnitude of the sampling signal is at or below an upper comparative signal threshold.

As noted above, theelectronics62 can adjust the level of attenuation provided by the outputoptical attenuator46 in response to the sampling signal. Theelectronics62 can adjust the level of attenuation provided by the dataoptical attenuator44 in response to the sampling signal in addition or as an alternative to adjusting the level of attenuation provided by the outputoptical attenuator46 in response to the sampling signal.

Suitable platforms for the chip include, but are not limited to, silica, indium phosphide, and silicon-on-insulator wafers.FIG.2 is a cross-section of portion of a chip constructed from a silicon-on-insulator wafer. A silicon-on-insulator (SOI) wafer includes a buriedlayer80 between asubstrate82 and a light-transmittingmedium84. In a silicon-on-insulator wafer, the buried layer is silica while the substrate and the light-transmitting medium are silicon. The substrate of an optical platform such as an SOI wafer can serve as the base for the entire chip. For instance, the optical components shown inFIG.1 can be positioned on or over the top and/or lateral sides of the substrate.

The portion of the chip illustrated inFIG.2 includes a waveguide construction that is suitable for use with chips constructed from silicon-on-insulator wafers. Aridge86 of the light-transmitting medium extends away fromslab regions88 of the light-transmitting medium. The light signals are constrained between the top of the ridge and the buried oxide layer.

The dimensions of the ridge waveguide are labeled inFIG.2. For instance, the ridge has a width labeled w and a height labeled h. A thickness of the slab regions is labeled T. For LIDAR applications, these dimensions are more important than other applications because of the need to use higher levels of optical power than are used in other applications. The ridge width (labeled w) is greater than 1 μm and less than 4 μm, the ridge height (labeled h) is greater than 1 μm and less than 4 μm, the slab region thickness is greater than 0.5 μm and less than 3 μm. These dimensions can apply to straight or substantially straight portions of the waveguide, curved portions of the waveguide and tapered portions of the waveguide(s). Accordingly, these portions of the waveguide will be single mode. However, in some instances, these dimensions apply to straight or substantially straight portions of a waveguide while curved portions of the waveguide and/or tapered portions of the waveguide have dimensions outside of these ranges. For instance, the tapered portions of theutility waveguide16 illustrated inFIG.1 can have a width and/or height that is >4 μm and can be in a range of 4 μm to 12 μm. Additionally or alternately, curved portions of a waveguide can have a reduced slab thickness in order to reduce optical loss in the curved portions of the waveguide. For instance, a curved portion of a waveguide can have a ridge that extends away from a slab region with a thickness greater than or equal to 0.0 μm and less than 0.5 μm. While the above dimensions will generally provide the straight or substantially straight portions of a waveguide with a single-mode construction, they can result in the tapered section(s) and/or curved section(s) that are multimode. Coupling between the multi-mode geometry to the single mode geometry can be done using tapers that do not substantially excite the higher order modes. Accordingly, the waveguides can be constructed such that the signals carried in the waveguides are carried in a single mode even when carried in waveguide sections having multi-mode dimensions. The waveguide construction ofFIG.2 is suitable for all or a portion of the waveguides selected from the group consisting of thecavity waveguide12,utility waveguide16,reference waveguide27,comparative waveguide30,first detector waveguide36,second detector waveguide38,sampling waveguide52,control waveguide57, andinterferometer waveguide60.

Thelight source10 that is interfaced with theutility waveguide16 can be a gain element that is a component separate from the chip and then attached to the chip. For instance, thelight source10 can be a gain element that is attached to the chip using a flip-chip arrangement.

Use of flip-chip arrangements is suitable when thelight source10 is to be interfaced with a ridge waveguide on a chip constructed from silicon-on-insulator wafer. Examples of suitable interfaces between flip-chip gain elements and ridge waveguides on chips constructed from silicon-on-insulator wafer can be found in U.S. Pat. No. 9,705,278, issued on Jul. 11, 2017 and in U.S. Pat. No. 5,991,484 issued on Nov. 23 1999; each of which is incorporated herein in its entirety. The constructions are suitable for use as thelight source10. When thelight source10 is a gain element, theelectronics62 can change the frequency of the outgoing LIDAR signal by changing the level of electrical current applied to through the gain element.

The attenuators can be a component that is separate from the chip and then attached to the chip. For instance, the attenuator can be included on an attenuator chip that is attached to the chip in a flip-chip arrangement. The use of attenuator chips is suitable for all or a portion of the attenuators selected from the group consisting of the data attenuator and the control attenuator.

As an alternative to including an attenuator on a separate component, all or a portion of the attenuators can be integrated with the chip. For instance, examples of attenuators that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in U.S. Pat. No. 5,908,305, issued on Jun. 1 1999; each of which is incorporated herein in its entirety. The use of attenuators that are integrated with the chip are suitable for all or a portion of the light sensors selected from the group consisting of the data attenuator and the control attenuator.

Light sensors that are interfaced with waveguides on a chip can be a component that is separate from the chip and then attached to the chip. For instance, the light sensor can be a photodiode, or an avalanche photodiode. Examples of suitable light sensor components include, but are not limited to, InGaAs PIN photodiodes manufactured by Hamamatsu located in Hamamatsu City, Japan, or an InGaAs APD (Avalanche Photo Diode) manufactured by Hamamatsu located in Hamamatsu City, Japan. These light sensors can be centrally located on the chip as illustrated inFIG.1. Alternately, all or a portion the waveguides that terminate at a light sensor can terminate at afacet18 located at an edge of the chip and the light sensor can be attached to the edge of the chip over thefacet18 such that the light sensor receives light that passes through thefacet18. The use of light sensors that are a separate component from the chip is suitable for all or a portion of the light sensors selected from the group consisting of thefirst light sensor40, the secondlight sensor42, the samplinglight sensor54, and thecontrol light sensor61.

As an alternative to a light sensor that is a separate component, all or a portion of the light sensors can be integrated with the chip. For instance, examples of light sensors that are interfaced with ridge waveguides on a chip constructed from a silicon-on-insulator wafer can be found in Optics Express Vol. 15, No. 21, 13965-13971 (2007); U.S. Pat. No. 8,093,080, issued on Jan. 10 2012; U.S. Pat. No. 8,242,432, issued Aug. 14 2012; and U.S. Pat. No. 6,108,8472, issued on Aug. 22, 2000 each of which is incorporated herein in its entirety. The use of light sensors that are integrated with the chip are suitable for all or a portion of the light sensors selected from the group consisting of thefirst light sensor40, the secondlight sensor42, the samplinglight sensor54, and thecontrol light sensor61.

Construction of optical gratings that are integrated with a variety of optical device platforms are available. For instance, a Bragg grating can be formed in a ridge waveguides by forming grooves in the top of the ridge and/or in the later sides of the ridge.

In some instances, it is desirable to scan the LIDAR output signal. The above chip construction is suitable for use with various scanning mechanisms used in LIDAR applications. For instance, the output LIDAR signal can be received by one or more reflecting devices and/or one more collimating devices. The one or more reflecting devices can be configured to re-direct and/or steer the LIDAR output signal so as to provide scanning of the LIDAR output signal. Suitable reflecting devices include, but are not limited to, mirrors such mechanically driven mirrors and Micro Electro Mechanical System (MEMS) mirrors. The one or more collimating devices provide collimation of the LIDAR output signal and can accordingly increase the portion of the LIDAR input signal that is received in theutility waveguide16. Suitable collimating devices include, but are not limited to, individual lenses and compound lenses.

FIG.3 illustrates the above chip used with a reflectingdevice90 and acollimating device92. For instance, a lens serves as a collimating device that receives the LIDAR output signal and provides collimation of the LIDAR output signal. A mirror serves as a reflectingdevice90 that receives the collimated LIDAR output signal and reflects the collimated LIDAR output signal in the desired direction. As is illustrated by the arrow labeled A, the electronics can move the mirror so as to steer the collimated LIDAR output signal and/or scan the collimated LIDAR output signal. The movement of the mirror can be in two dimensions or three dimensions. Suitable mirrors include, but are not limited to, mechanically driven mirrors and Micro Electro Mechanical System (MEMS) mirrors.

FIG.4 illustrates the above chip used with a reflectingdevice90 and acollimating device92. For instance, a mirror serves as a reflectingdevice90 that receives the LIDAR output signal and reflects the LIDAR output signal in the desired direction. As is illustrated by the arrow labeled A, the electronics can move the mirror so as to steer the LIDAR output signal and/or scan the LIDAR output signal. A lens serves as acollimating device92 that receives the LIDAR output signal from the mirror and provides collimation of the LIDAR output signal. The lens can be configured to move with the movement of the mirror so the lens continues to receive the LIDAR output signal at different positions of the mirror. Alternately, the movement of the mirror can be sufficiently limited that the lens continues to receive the LIDAR output signal at different positions of the mirror. The movement of the mirror can be in two dimensions or three dimensions. Suitable mirrors include, but are not limited to, mechanically driven mirrors and Micro Electro Mechanical System (MEMS) mirrors.

Technologies such as SOI MEMS (Silicon-On-Insulator Micro Electro Mechanical System) technology can be used to incorporate a reflecting device such as a MEMS mirror into the chip. For instance,FIG.5 is a cross section of a portion of the chip taken through the longitudinal axis of theutility waveguide16. The illustrated chip was constructed on silicon-on-insulator waveguide. A mirror recess extends through the light-transmitting medium to the base. The mirror is positioned in the mirror recess such that the mirror receives the LIDAR output signal from the utility waveguide. A lens serves as acollimating device92 that receives the LIDAR output signal from the mirror and provides collimation of the LIDAR output signal. The lens can be configured to move with the movement of the mirror so the lens continues to receive the LIDAR output signal at different positions of the mirror. Alternately, the movement of the mirror can be sufficiently limited that the lens continues to receive the LIDAR output signal at different positions of the mirror. The electronics can control movement of the mirror in two or three dimensions.

The above chips can be modified so that the data branch includes one or more secondary branches and one or more secondary balanced detectors that can be employed to refine the optical data provided to the electronics. The reference signal and the comparative signal can be divided among the different balanced detectors. For instance,FIG.6A illustrates the above chip modified to include two different balanced detectors. Afirst splitter102 divides the reference signal carried on thereference waveguide27 onto afirst reference waveguide110 and asecond reference waveguide108. Thefirst reference waveguide110 carries a first portion of the reference signal to the light-combiningcomponent28. Thesecond reference waveguide108 carries a second portion of the reference signal to a second light-combiningcomponent112.

Asecond splitter100 divides the comparative signal carried on thecomparative waveguide30 onto a firstcomparative waveguide104 and a secondcomparative waveguide106. The firstcomparative waveguide104 carries a first portion of the comparative signal to the light-combiningcomponent28. The secondcomparative waveguide108 carries a second portion of the comparative signal to the second light-combiningcomponent112.

The second light-combiningcomponent112 combines the second portion of the comparative signal and the second portion of the reference signal into a second composite signal. The light-combiningcomponent112 also splits the resulting composite signal onto a firstauxiliary detector waveguide114 and a secondauxiliary detector waveguide116.

The firstauxiliary detector waveguide114 carries a first portion of the second composite signal to a first auxiliarylight sensor118 that converts the first portion of the second composite signal to a first auxiliary electrical signal. The secondauxiliary detector waveguide116 carries a second portion of the second composite signal to a second auxiliarylight sensor120 that converts the second portion of the second composite signal to a second auxiliary electrical signal. Examples of suitable light sensors include germanium photodiodes (PDs), and avalanche photodiodes (APDs).

Thefirst reference waveguide110 and thesecond reference waveguide108 are constructed to provide a phase shift between the first portion of the reference signal and the second portion of the reference signal. For instance, thefirst reference waveguide110 and thesecond reference waveguide108 can be constructed so as to provide a 90 degree phase shift between the first portion of the reference signal and the second portion of the reference signal. Accordingly, one of the reference signal portions can be a sinusoidal function and the other reference signal portion can be a cosine function. In one example, thefirst reference waveguide110 and thesecond reference waveguide108 are constructed such that the first reference signal portion is a cosine function and the second reference signal portion is a sinusoidal function. Accordingly, the portion of the reference signal in the first composite signal is phase shifted relative to the portion of the reference signal in the second composite signal, however, the portion of the comparative signal in the first composite signal is not phase shifted relative to the portion of the comparative signal in the second composite signal.

Thefirst light sensor40 and the secondlight sensor42 can be connected as a balanced detector and the first auxiliarylight sensor118 and the second auxiliarylight sensor120 can also be connected as a balanced detector. For instance,FIG.6B provides a schematic of the relationship between thedata module64 of theelectronics62, thefirst light sensor40, the secondlight sensor42, the first auxiliarylight sensor118, and the second auxiliarylight sensor120. The symbol for a photodiode is used to represent thefirst light sensor40, the secondlight sensor42, the first auxiliarylight sensor118, and the second auxiliarylight sensor120 but one or more of these sensors can have other constructions.

The electronics connect thefirst light sensor40 and the secondlight sensor42 as a firstbalanced detector124 and the first auxiliarylight sensor118 and the second auxiliarylight sensor120 as a secondbalanced detector126. In particular, thefirst light sensor40 and the secondlight sensor42 are connected in series. Additionally, the first auxiliarylight sensor118 and the second auxiliarylight sensor120 are connected in series. The serial connection in the first balanced detector is in communication with afirst data line128 that carries the output from the first balanced detector as a first data signal. The serial connection in the second balanced detector is in communication with asecond data line132 that carries the output from the first balanced detector as a second data signal.

Thefirst data line128 carries the first data signal to atransform module136 and thesecond data line132 carries the second data signal to thetransform module136. The transform module is configured to perform a complex transform on a complex signal so as to convert the input from the time domain to the frequency domain. The first data signal can be the real component of the complex signal and the second data signal can be the imaginary component of the complex. The transform module can execute the attributed functions using firmware, hardware and software or a combination thereof.

The solid line inFIG.6C provides an example of the output of the transform module when a Complex Fourier transform converts the input from the time domain to the frequency domain. The solid line shows a single frequency peak. The frequency associated with this peak is used by the data module as the frequency of the LIDAR input signal.

The data module uses this frequency for further processing to determine the distance and/or radial velocity of the reflecting object.FIG.6C also includes a second peak illustrated by a dashed line. Prior methods of resolving the frequency of the LIDAR input signal made use of real Fourier transforms rather than the Complex Fourier transform technique disclosed above. These prior methods output both the peak shown by the dashed line and the solid line. As noted above, when using LIDAR applications, it can become difficult to identify the correct peak. Since the above technique for resolving the frequency generates a single solution for the frequency, the inventors have resolved the ambiguity with the frequency solution.

The data module use the single frequency that would be present inFIG.6C to determine the distance of the reflecting object from the chip and/or the radial speed between the object and the chip. For instance, the following equation applies during a sample where electronics increase the frequency of the outgoing LIDAR signal: +f_ub=−f_d+ατ₀where f_ubis the frequency provided by the transform module, f_drepresents the Doppler shift (f_d=2νf_ν/c) where f_cis the frequency of the LIDAR output signal, ν is the radial velocity of the reflecting object relative to the chip where the direction from the reflecting object toward the chip is assumed to be the positive direction, and c is the speed of light, α is defined below, and τ₀is the roundtrip delay for a stationary reflecting object. The following equation applies during a sample where electronics decrease the frequency of the outgoing LIDAR signal: −f_db=−f_d−ατ₀where f_dbis the frequency provided by the transform module. In these two equations, ν and τ₀are unknowns. The electronics solve these two equations for the two unknowns.

Suitable electronics can include, but are not limited to, a controller that includes or consists of analog electrical circuits, digital electrical circuits, processors, microprocessors, digital signal processors (DSPs), computers, microcomputers, or combinations suitable for performing the operation, monitoring and control functions described above. In some instances, the controller has access to a memory that includes instructions to be executed by the controller during performance of the operation, control and monitoring functions. Although the electronics are illustrated as a single component in a single location, the electronics can include multiple different components that are independent of one another and/or placed in different locations. Additionally, as noted above, all or a portion of the disclosed electronics can be included on the chip including electronics that are integrated with the chip.

A single light sensor can replace the second balanced detectorfirst light sensor40 and the secondlight sensor42 and/or a second light sensor can replace the first auxiliarylight sensor118 and the second auxiliarylight sensor120. When a single light sensor replaces thefirst light sensor40 and the secondlight sensor42, the light-combiningcomponent28 need not include light-splitting functionality. As a result, the illustrated light light-combiningcomponent28 can be a 2×1 light-combining component rather than the illustrated 2×1 light-combining component. For instance, the illustrated light light-combining component can be a 2×1 MMI device. In these instances, the chip includes a single detector waveguide that carries the composite signal to the light sensor.

When a single light sensor replaces the first auxiliarylight sensor118 and the second auxiliarylight sensor120, second light-combiningcomponent112 need not include light-splitting functionality. As a result, the illustrated second light-combiningcomponent112 can be a 2×1 light-combining component rather than the illustrated 2×2 light-combining component. For instance, the illustrated light light-combining component can be a 2×1 MMI device. In these instances, the chip includes a single detector waveguide that carries the composite signal from the second light-combiningcomponent112 to the light sensor.

A vehicle can include one or more of the LIDAR chips. For instance, a car that has an ADAS (Advanced Driver Assistance System) and/or a self-driving vehicle can have an optical sensor system with a LIDAR module that includes, consists of, or consists essentially of one or more of the LIDAR chips. As an example,FIG.7 is a diagram of a vehicle that includes aheadlight150 and atrunk152. The car includes aLIDAR module154 located near theheadlight150. For instance, theLIDAR module154 can be located above, below, and/or beside theheadlight150. AlthoughFIG.7 illustrates the car having a single LIDAR module, the car can include multiple LIDAR modules. Each of the modules can include or consist of one or more LIDAR chips.

The car also includes a storage region that is remote from theLIDAR module154 such as a compartment that is accessible from the trunk of a car. A communications link156 provides communication between one ormore LIDAR chips157 included in theLIDAR module154 andremote electronics158 located in the storage region. The storage region is generally selected to protect theremote electronics158 from the environment and, in some instances, to provide thermal control of theremote electronics158. In addition to processing signals from one or more LIDAR modules, theremote electronics158 generally processes the signals from a variety of different sensors in the vehicle. For instance, theremote electronics158 can process signals from cameras, inertial sensors, rotational sensors, radar, infra-red (IR) cameras, radionavigation systems such as the Global Positioning System (GPS), and acoustic sensors such as microphones.

Due to the configuration of many vehicles, a communications link that is several meters long is often needed to make the circuitous route from a LIDAR module to the remote electronics. In many instances, the communication link needs to provide a data rate of more than 0.1 Gbps, more than 10 Gbps or even more than 20 Gbps for a length greater than 5 m, 10 m, or even 20 m as can occur in vehicles such a large trucks. Copper wires are often ineffective for carrying data at these rates over these lengths. Additionally, copper wires and cables for these data rates over these distances add greater weight to an autonomous vehicle and also generate more electromagnetic interference (EMI) and are more susceptible to EMI from other data signals. This is important for all autonomous vehicles, but will be especially important for airborne autonomous vehicles. A communication link that includes or consists of one or more optical fibers can provide the needed data rates at lengths longer than 5 m, 10 m, or 20 m. Additionally or alternately, a communication link that includes or consists of an optical fiber can be less than 100 m, 200 m, or 500 m.

Theelectronics62 disclosed in the context ofFIG.1 throughFIG.6C can be divided between theremote electronics158 andlocal electronics160. All or a portion of the local electronics can be in the proximity of theLIDAR module154. In some instances, all or a portion of the local electronics are included on one or more LIDAR chips in theLIDAR module154. In some instances, all or a portion of the local electronics are included on one or more LIDAR chips in theLIDAR module154. In some instances, all or a portion of the local electronics are included inside of packaging for theLIDAR module154. In some instances, all or a portion of the local electronics are immobilized on packaging for theLIDAR module154. Accordingly, the distance between thelocal electronics160 and theLIDAR module154 is less than the distance between theremote electronics158 and theLIDAR module154.

As noted above, theelectronics62 can include one or more modules selected from a group consisting of asource control module63, adata module64, apower module65, and adata control module66. In some instances, thelocal electronics160 includes one, two, or three modules selected from the group consisting of thesource control module63,data module64,power module65, anddata control module66 and theremote electronics158 includes one two or three modules selected from the group consisting of thesource control module63,data module64,power module65, anddata control module66.

In one example, thelocal electronics160 include thesource control module63,data module64,power module65, anddata control module66 and theremote electronics158 include thedata module64. Accordingly, theremote electronics158 can include a portion of the components from the LIDAR chip illustrated above. For instance, when theremote electronics158 include thedata module64, theremote electronics158 can include thefirst light sensor40 and the secondlight sensor42 of the LIDAR chips disclosed in the context ofFIG.1 throughFIG.6C. Accordingly, theremote electronics158 can include a balanced photodetector that includes thefirst light sensor40 and the secondlight sensor42 as illustrated inFIG.8. In some instances, theremote electronics158 can include the first auxiliarylight sensor118 and second auxiliarylight sensor120 in addition to thefirst light sensor40 and the secondlight sensor42 as disclosed in the context ofFIG.6A throughFIG.6B. Accordingly, theremote electronics158 can include a balanced photodetector that includes thefirst light sensor40 and the secondlight sensor42 and a second balanced photodetector that includes the first auxiliarylight sensor118 and the second auxiliarylight sensor120 as illustrated inFIG.9.

When theremote electronics158 can include one or more light sensors selected from the group consisting of thefirst light sensor40, the secondlight sensor42, the first auxiliarylight sensor118 and the second auxiliarylight sensor120, the communications link156 can include one or more optical fibers. For instance,FIG.8 shows the communications link156 having a firstoptical fiber164 that guides the first portion of the composite sample signal to theremote electronics158 and a secondoptical fiber165 that guides the second portion of the composite sample signal to theremote electronics158. Theremote electronics158 include awaveguide170 that guides the first portion of the composite sample signal to thefirst light sensor40 and awaveguide170 that guides the second portion of the composite sample signal to the secondlight sensor42.

FIG.9 shows the LIDAR chip ofFIG.6A modified to be used with a communications link156 that includes a firstoptical fiber164 that guides the first portion of the composite sample signal to theremote electronics158 and a secondoptical fiber165 that guides the second portion of the composite sample signal to theremote electronics158, a thirdoptical fiber166 that guides the first portion of the second composite signal to theremote electronics158 and a fourthoptical fiber167 that guides the second portion of the second composite signal to theremote electronics158. Theremote electronics158 includes a waveguide that guides the first portion of the composite sample signal to thefirst light sensor40, a waveguide that guides the second portion of the composite sample signal to the secondlight sensor42, a waveguide that guides the first portion of the second composite signal to the first auxiliarylight sensor118, and a waveguide that guides the second portion of the second composite signal to the second auxiliarylight sensor120. It is currently believed that a vehicle having a LIDAR chip and communications link156 constructed according toFIG.9 will carry data at rate of about 24 Gbps for two or more meters and possibly as many as 20 m. Over these distances, copper materials cannot effectively carry data at an equivalent of these digital rates.

When the optical link includes one or more optical fibers, the LIDAR chip can include anoptical port162 for providing optical communication between a waveguide on the LIDAR chip and the optical fiber. An optical signal can exit from the LIDAR chip through an optical port. For instance, a suitable optical port includes the waveguide ending at a facet through which an optical signal exits from the LIDAR chip. For instance, one or more waveguide selected from a group consisting of afirst detector waveguide36, asecond detector waveguide38, a firstauxiliary detector waveguide114 and a secondauxiliary detector waveguide116 can terminate at a facet that is optically aligned with a facet of an optical fiber. An optical port can be constructed such that a light signal output from the port exits the LIDAR chip above the LIDAR chip, below the LIDAR chip, or from an edge of the LIDAR. Although the optical port is disclosed in the context of optical signals exiting from the LIDAR chip, the LIDAR chip can additionally or alternately be operated such that light signals enter the LIDAR chip through an optical port. Suitable constructions of optical ports that providing optical communication between a waveguide and an optical fiber include, but are not limited to, U.S. Pat. No. 6,108,472, filed on Feb. 6, 1998, given Ser. No. 09/019,729, entitled “Device for Re-directing Light From Optical Waveguide,” and incorporated herein in its entirety and in U.S. Pat. No. 7,245,803, filed on Feb. 10, 2004, given Ser. No. 10/776,475, entitled “Optical Waveguide Grating Coupler,” and incorporated herein in its entirety.

In the LIDAR chip ofFIG.8 andFIG.9, one or more light signals (LIDAR data signals) selected from the group consisting of the first portion of the composite sample signal, the second portion of the composite sample signal, the first portion of the second composite signal, and second portion of the second composite signal exit the LIDAR chip through an optical port. Each of these light signals includes light from the reflected signal. Accordingly, the light signal(s) that exit the LIDAR chip through an optical port can include light from the reflected signal. The first portion of the composite sample signal, the second portion of the composite sample signal, the first portion of the second composite signal, and the second portion of the second composite signal also include light from the reference signal. Accordingly, the light signal(s) that exit the LIDAR chip through an optical port can additionally or alternately include light from a reference signal and/or light that is not reflected by an object. The light signal(s) that exit the LIDAR chip through an optical port can be digital or analog. However, the first portion of the composite sample signal, the second portion of the composite sample signal, the first portion of the second composite signal, and second portion of the second composite signal have not undergone digital processing and are accordingly analog signals. As a result, the light signal(s) that exit the LIDAR chip through an optical port can be analog signals that undergo digital processing off the chip and/or at theremote electronics158.

Although the optical port is disclosed in the context of providing optical signals for a data module included in the remote electronics, a LIDAR chip can include one or more optical ports for other applications. For instance, a LIDAR chip can include an optical port that transmits optical signals for asource control module63,power module65, and/ordata control module66.

FIG.8 andFIG.9 illustrate the optical components from the LIDAR chip ofFIG.1 andFIG.6A distributed between the LIDAR chip and the remote electronics. As an example, inFIG.8, the remote electronics includes thefirst light sensor40 and the secondlight sensor42 from the LIDAR chip illustrated inFIG.1. However other distributions of the optical components between the LIDAR chip and the remote electronics can be employed. As an example, the remote electronics can include the first light-combiningcomponent28, thefirst detector waveguide36, thesecond detector waveguide38, thefirst light sensor40, and the secondlight sensor42 from the LIDAR chip illustrated inFIG.1 and the remote electronics can have these optical components configured to operate as disclosed in the context ofFIG.1. In such an embodiment, the LIDAR chip can include an optical port through which the reference signal exits from the LIDAR chip and is received by the communication link. The LIDAR chip can include an optical port through which the comparative signal exits from the LIDAR chip. The communication link can then carry these light signals to the optical components on the remote electronics which can then process these light signals as disclosed in the context ofFIG.1. Other possible distributions of the optical components between the LIDAR chip and the remote electronics are disclosed in U.S. patent application Ser. No. 16/113,364, filed on Aug. 27, 2018, entitled “Optical Sensor System” and incorporated herein in its entirety.

The LIDAR system ofFIG.6A andFIG.9A can be operated as described above so as to approximate the LIDAR data, however, other configurations are possible. For instance, a LIDAR chip constructed according toFIG.6A and/orFIG.9A and/or having optical components arranged according toFIG.6A and/orFIG.9A but distributed between the LIDAR chip and the remote electronics can be modified to include a modulator and operated so as to generate LIDAR data as is disclosed in U.S. Patent Application Ser. No. 62/727,453, filed on Sep. 5, 2015, and incorporated herein in its entirety and/or as disclosed in U.S. Patent Application Ser. No. 62/726,101, filed on Aug. 31, 2018.

In some instances, thelocal electronics160 perform processing of one or more light signals on the LIDAR chip and then use components on the LIDAR to generate an optical data signal that includes data generated from these light signals. The electronics can transmit the optical data signal to theremote electronics158 for additional processing. In some instances, the optical data signal is a digital signal. The one or more light signals processed by thelocal electronics160 can be analog light signals. For instance, thelocal electronics160 can process one or more of the LIDAR data signals (composite sample signal, the second portion of the composite sample signal, the first portion of the second composite signal, and second portion of the second composite signal). In some instances, thelocal electronics160 process one or more of the LIDAR data signals so as to determine the distance and/or radial velocity between the reflecting object and the chip and/or vehicle. Thelocal electronics160 can then use one or more components on the LIDAR chip to generate an optical data signal that indicates the resulting radial velocity and/or distance. The optical data signal can be received on the communications link156 which carries the optical data signal to theremote electronics158.

FIG.10 illustrates the LIDAR chip ofFIG.1 modified to include adata processing branch208 for generation and transmission of an optical data signal that is transmitted from the LIDAR chip to theremote electronics158 on the communications link156. Theremote electronics158 and thelocal electronics160 include the functionality of theelectronics62 as indicated by the dashed line around theremote electronics158 and thelocal electronics160. As is evident from the above discussion, the dashed line being around theremote electronics158 and thelocal electronics160 does not indicate a common location for theremote electronics158 and thelocal electronics160 although a common location is possible.

Thedata processing branch208 can include a laser cavity. For instance, the illustrateddata processing branch208 includes adata light source210 that can include or consist of a data gain medium (not shown) for a laser. The LIDAR chip also includes adata cavity waveguide212 that receives a light signal from the datalight source210. The datalight source210 can be positioned in adata recess213 so a facet of the datalight source210 is optically aligned with a facet of thedata cavity waveguide212 to allow the datalight source210 anddata cavity waveguide212 to exchange light signals. Thedata cavity waveguide212 carries the light signal to apartial return device214. The illustratedpartial return device214 is an optical grating such as a Bragg grating. However, otherpartial return devices214 can be used; for instance, mirrors can be used in conjunction with echelle gratings and arrayed waveguide gratings.

Thepartial return device214 returns a return portion of the light signal to thedata cavity waveguide212 as a return signal. For instance, thedata cavity waveguide212 returns the return signal to the datalight source210 such that the return portion of the light signal travels through the data gain medium. The datalight source210 is configured such that at least a portion of the return signal is added to the light signal that is received at thedata cavity waveguides12. For instance, the datalight source210 can include a highly, fully, or partiallyreflective device215 that reflects the return signal received from the gain medium back into the gain medium. As a result, light can resonate between thepartial return device214 and thereflective device215 so as to form a laser cavity such as a Distributed Bragg Reflector (DBR) laser cavity. A DBR laser cavity has an inherently narrow-linewidth and a longer coherence length than DFB lasers and accordingly improves performance when an object reflecting the LIDAR output signal from the chip is located further away from the chip.

Thepartial return device214 passes a portion of the light signal received from thedata cavity waveguide212 to adata waveguide216 included on the chip. In some instances, thedata waveguide216 includes ataper220 such as thetaper20 optionally included in the utility waveguide. The portion of the light signal that thedata waveguide216 receives from thepartial return device214 serves as the output of the data laser cavity. The output of the data laser cavity serves as an outgoing data signal on thedata waveguide216. The data waveguide216 terminates at afacet218 and carries the outgoing data signal to thefacet218. Thefacet218 can be positioned such that the outgoing data signal traveling through thefacet218 exits the LIDAR chip and serves as an optical data signal. For instance, thefacet218 can be positioned at an edge of the chip so the outgoing data signal traveling through thefacet218 exits the LIDAR chip and serves as the optical data signal.

The LIDAR chip also includes amodulator246 positioned along the data waveguide216 such that theelectronics62 can modulate the outgoing data signal. Accordingly, theelectronics62 can include a data processing module (not shown) configured to operate themodulator246 so as to encode data onto the outgoing data signal and accordingly onto the optical data signal. In some instances, the data encoded onto the outgoing data signal was data generated from the LIDAR data signals. Examples of a modulators suitable for use with a LIDAR chip and/or a LIDAR chips constructed on silicon-on-insulator platforms include, but are not limited to, the modulators disclosed in U.S. patent application Ser. No. 12/653,547, filed on Dec. 15, 2009, granted U.S. Pat. No. 8,346,028, entitled “Optical Device Having Modulator Employing Horizontal Electrical Field,” and incorporated herein in its entirety.

The data processing branch includes adirectional coupler256 that moves a portion of the outgoing data signal from the data waveguide216 onto acontrol waveguide258. The coupled portion of the outgoing data signal serves as a tapped signal. AlthoughFIG.10 illustrates adirectional coupler256 moving portion of the outgoing data signal onto thecontrol waveguide258, other signal-tapping components can be used to move a portion of the outgoing data signal from the data waveguide216 onto thecontrol waveguide258. Examples of suitable signal tapping components include, but are not limited to, y-junctions, and MMIs.

Thecontrol waveguide258 carries the tapped signal to acontrol light sensor260 that converts the control light signal to an electrical signal that serves as an electrical control signal. Examples of suitable controllight sensors260 include, but are not limited to, PN and PIN types of germanium photodiodes (PDs) and InGaAs photodiodes.

Theelectronics62 can include a data source control module (not shown) configured to control the output of the datalight source210. For instance, the data source control module can be configured to tune the output of the datalight source210 in response to the electrical control signal from thecontrol light sensor260. For instance, the data source control module can tune the power of the outgoing data signal in response to the electrical control signal from thecontrol light sensor260. In some instances, the data source control module increase the power of the outgoing data signal in response to magnitude of the electrical control signal from thecontrol light sensor260 falling below a lower power threshold and/or decrease the power of the outgoing data signal in response to magnitude of the electrical control signal from thecontrol light sensor260 rising above an upper power threshold. This functionality allows the data source control module to set the laser control parameters for optimal performance and adjust for changes in the performance of the datalight source210 due to other effects such as the passage of time and/or changes in temperature.

AlthoughFIG.10 illustrates the LIDAR chip ofFIG.1 modified to include a data processing branch, other LIDAR chips can be modified to include a data processing branch. For instance,FIG.11 illustrates the LIDAR chip ofFIG.6A throughFIG.6C modified to include a data processing branch.

The data processing branch allows theelectronics62 to perform localized processing of data from the LIDAR chip and transmit resulting data to the to theremote electronics158 on the communications link156. For instance, thelocal electronics160 can receive one or more electronic data signals selected from the group consisting of the first electrical signal, the second electrical signal, the first auxiliary electrical signal, and the second auxiliary electrical signal (electronic LIDAR data signals). Thelocal electronics160 can process the received electronic LIDAR data signals as discussed above to determine LIDAR data such as the distance and/or radial velocity between the chip and/or vehicle. Thelocal electronics160 can operate the datalight source210 so as to generate the outgoing data signal on thedata waveguide216. Thelocal electronics160 can also operate themodulator246 so as to encode the LIDAR data (distance and/or radial velocity between the reflecting object and the chip and/or vehicle) onto the outgoing data signal and accordingly on the optical data signal. The optical data signal is received by the communications link156 which carriers the optical data signal to theremote electronics158. In this example, the electronic LIDAR data signals are analog signals. However, thelocal electronics160 can encode the data onto the outgoing data signal as a digital signal or as an analog signal. Accordingly, thelocal electronics160 can receive analog signals but generate a digital optical data signal. As a result, in some instances, thelocal electronics160 provide digital processing of the data from the LIDAR chip. In some instances, thelocal electronics160 receive analog signals and generate an analog optical data signal. For instance, thelocal electronics160 can receive an analog electrical signal from the data branch and encode the received electrical signal onto the optical data signal. As an example, the electronics can receive the first electrical signal and encode the first electrical signal onto an outgoing optical signal and can also receive the second electrical signal and encode the second electrical signal onto another outgoing optical signal. In these examples, the data processing module can include or consist of a modulator driver configured to drive themodulator246.

In the above example, the LIDAR module transmits LIDAR data to theremote electronics158. Additionally or alternately, the data processing branch can be constructed to transmit other data to theremote electronics158 provided by other sensors co-located with the LIDAR chip. Examples of other data that the data processing branch can transmit to theremote electronics158 include, but are not limited to, temperature at one or more locations on the LIDAR chip, orientation of the LIDAR chip, and error diagnosis signals.

The LIDAR chip can generate more than one optical data signal. For instance, the LIDAR chip can include more than one data processing branch associated with eachdata branch24. Each of the different optical data signals can exit the LIDAR chip from adifferent facet218 and/or a differentoptical port162. The communications link156 can include multiple optical fibers that each receives one of the optical data signals.

In some instances, the LIDAR chip include adata processing branch208 that generates multiple different outgoing data signals and combines them into a composite outgoing data signal that is received by the communications link156. For instance, the LIDAR chip ofFIG.12A includes multiple datalight sources210 that are each the source of a different outgoing data signal on adata waveguide216. The LIDAR chip also includes anoptical combiner276 that combines the different outgoing data signals so as to form a composite outgoing data signal. The composite outgoing data signal is received on asecondary data waveguides277 that carries the composite outgoing data signal to anoptical port162 from which the composite outgoing data signal exits from the LIDAR chip as an optical data signal. The optical data signal is received by the communications link156. The different outgoing data signals can have different wavelengths to enable theremote electronics158 to process the data fromdifferent processing branches208 as if they are different channels.

In some instances, the data processing branch is configured to generate multiple different optical data signals. As an example,FIG.12B illustrates the LIDAR chip ofFIG.10 modified to generate multiple different optical data signals. The data waveguide216 carries the outgoing data signal to anoptical splitter278 that divides the outgoing data signal into multiple secondary data signals.Secondary data waveguides280 each receives one of the secondary data signals. Amodulator246 is positioned along each of thesecondary data waveguides280 and are each configured such that thelocal electronics160 can modulate one of the secondary data signals. Accordingly, thelocal electronics160 can encode different data onto each of the secondary data signals. Each of the secondary data signals can exit from the LIDAR chip through a facet and can serve as a different optical data signal. When the LIDAR chip generates multiple optical data signals, the communications link156 can include multiple optical fibers that each receive one of the optical data signals.

Thelight source10 and the datalight source210 in the above LIDAR chips can have the same or different wavelengths. In some instances, thelight source10 and the datalight source210 have different wavelengths to reduce cross talk.

Although thelight source10 and the datalight source210 are shown positioned in different recesses (13 and213), thelight source10 and the datalight source210 can be positioned in the same recess. Although thelight source10 and the datalight source210 are shown as separate from one another, thelight source10 and the datalight source210 can share certain components. For instance, thelight source10 and the datalight source210 can be constructed on the same gain medium. In some instances, the helight source10 and/or the datalight source210 are each constructed on a different chip that is attached to the LIDAR chip. In some instances, thelight source10 and the datalight source210 are hybridized on the LIDAR chip using an active array such as an RSOA array. In some instances, the RSOA array also includes thepartial return device14 and thepartial return device214. In some instances, thelight source10 and the datalight source210 are hybridized on the LIDAR chip using an active array such as a DFB array.

InFIG.9 throughFIG.12B, the LIDAR chip is configured such that thedata processing branch208 is optically isolated from the LIDAR branch in that thedata processing branch208 does not exchange light signals with the LIDAR branch. For instance, the one or moredata processing branches208 on the LIDAR chip do not exchange light signals with the portion of the LIDAR chip that generates the one or more composite signals. In these instances, the local electronics provide communication between the one or moredata processing branches208 and the LIDAR branch. In some instances, the LIDAR chip is configured such that thedata processing branch208 is in optical communication with the LIDAR branch.

The functionality of theelectronics62 can be divided between thelocal electronics160 and theremote electronics158.FIG.13 illustrates one example of the distribution of the electronics functionality between thelocal electronics160 and theremote electronics158. The local electronics include thesource control module63, thedata module64, thepower module65, thedata control module66, the data source control module292, and the data processing module294. As is evident fromFIG.13, in some instances, thedata module64 uses signals from the data branch to generate LIDAR data such as the distance and/or radial velocity between a reflecting object and/or chip and/or vehicle. The data processing module294 can receive the LIDAR data from thedata module64. The data processing module294 can use the data processing branch to transmit an optical data signal that includes the data to theremote electronics158 over the communications link156. As is evident fromFIG.13, theremote electronics158 can include alight sensor296 that receives the optical data signal. Thelight sensor296 can output an electrical signal generated in response to the optical data signal. For instance, thelight sensor296 can convert the optical data signal to a remote electrical data signal. The remote theremote electronics158 can include aremote processing module296 for further processing of the remote electrical data signal.

Suitable electronics for inclusion in theelectronics62, thelocal electronics160 and/or theremote electronics158 can include, but are not limited to, a controller that includes or consists of analog electrical circuits, digital electrical circuits, processors, microprocessors, digital signal processors (DSPs), computers, microcomputers, or combinations suitable for performing the operation, monitoring and control functions described above. In some instances, the controller has access to a memory that includes instructions to be executed by the controller during performance of the operation, control and monitoring functions. Although the electronics are illustrated as a single component in a single location, the electronics can include multiple different components that are independent of one another and/or placed in different locations. Additionally, as noted above, all or a portion of the disclosed electronics can be included on the chip including electronics that are integrated with the chip.

Although the laser cavity and/or the data laser cavity is shown as being positioned on the chip, all or a portion of the laser cavity and/or the data laser cavity can be located off the chip. For instance, theutility waveguide16 can terminate at a second facet through which the outgoing LIDAR signal can enter theutility waveguide16 from a laser cavity located off the chip.

The above chips can include components in addition to the illustrated components. As one example, optical attenuators (not illustrated) can be positioned along thefirst detector waveguide36 and thesecond detector waveguide38. The electronics can operate these attenuators so the power of the first portion of the composite sample signal that reaches thefirst light sensor40 is the same or about the same as the power of the second portion of the composite sample signal that reaches the secondlight sensor42. The electronics can operate the attenuators in response to output from thefirst light sensor40 which indicates the power level of the first portion of the composite sample signal and the secondlight sensor42 which indicates the power level of the second portion of the composite sample signal.

Although the optical sensor system is disclosed in the context of a vehicle such as car, the optical sensor system can be included in other vehicles. Suitable vehicles include, but are not limited to, trucks, boats, planes, spacecraft, and undersea craft. The vehicle need not be for transportation of people. For instance, the vehicle can be for the transportation of commercial goods, emergency food and medical supplies, and building materials. The optical sensor system can also be used in applications other than vehicles. For instance, the optical sensor system can be employed in other forms of autonomous mobile robots that do not carry people or goods but are used for numerous activities such as surveying, monitoring and maintenance.

Although the optical sensor system is disclosed as including local electronics that are located off the LIDAR chip, all or a portion of the local electronics can be on the LIDAR chip and/or integrated with the LIDAR chip.

Although not shown, the optical sensor system can include a LIDAR chip with one or moreoptical ports162 through which digital light signals are transmitted and one or more optical ports through which analog light signals are transmitted. For instance, the LIDAR chip can include one or more data light sources for generating optical data signals and can also include one or moreoptical ports162 through which analog light signals are transmitted as disclosed in the context ofFIG.8 throughFIG.9.

Other embodiments, combinations and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.

Claims (18)

The invention claimed is:

1. A LIDAR system, comprising:

a LIDAR chip; and

local electronics that receive a beating signal from the LIDAR chip, the local electronics generating LIDAR data from a frequency of the beating signal,

the LIDAR data indicating a distance and/or a radial velocity between the LIDAR system and a reflecting object located outside of the LIDAR system,

the electronics operating one or more components on the LIDAR chip such that the LIDAR chip transmits an optical data signal carrying the LIDAR data.

2. The system ofclaim 1, wherein the local electronics are included on the LIDAR chip.

3. The system ofclaim 1, wherein the signal received from the LIDAR chip is an analog signal.

4. The system ofclaim 1, wherein the optical data signal is a digital signal.

5. The system ofclaim 1, wherein the signal received from the LIDAR chip is an analog signal and the optical data signal is a digital signal.

6. The system ofclaim 1, wherein the optical data signal exits from the LIDAR chip and is received at an optical fiber.

7. The system ofclaim 1, wherein the LIDAR chip is configured to output a LIDAR output signal that is reflected off a reflecting object located of the LIDAR chip and to receive a portion of the reflected light as a LIDAR input signal.

8. The system ofclaim 7, wherein the LIDAR chip includes multiple laser cavities.

9. The system ofclaim 1, wherein the LIDAR chip is configured to guide an outgoing LIDAR signal and to output a LIDAR output signal that can be reflected off a reflecting object located of the LIDAR chip, the LIDAR output signal including light from the outgoing LIDAR signal;

the LIDAR chip configured to receive a portion of the reflected LIDAR output signal light as a LIDAR input signal.

10. The system ofclaim 9, wherein the beating signal that the local electronics receive from the LIDAR chip is an electrical signal.

11. The system ofclaim 10, wherein the electrical signal is generated from a light signal that includes light from the LIDAR input signal.

12. The system ofclaim 11, wherein the LIDAR chip is configured to generate a composite light signal that includes light from a comparative signal and light from a reference signal,

the reference signal including light from the outgoing LIDAR signal that has not exited from the LIDAR chip,

the comparative signal including light from the LIDAR input signal.

13. The system ofclaim 12, wherein the electrical signal is generated from the composite signal.

14. The system ofclaim 12, wherein the LIDAR chip includes a first optical component and a second optical component,

the first optical component configured to combines a first portion of the reference signal with a first portion of the comparative signal,

the second optical component configured to combine a second portion of the reference signal with a second portion of the comparative signal, and

the second portion of the reference signal being phase shifted relative to the first portion of the reference signal.

15. The system ofclaim 1, wherein the signal received from the LIDAR chip is one of multiple signals that the local electronics receive from the LIDAR chip,

the signals received from the LIDAR chip including a first data electrical signal and a second data electrical signal,

the first data electrical signal being generated from a light signal that includes light from the first portion of the reference signal and the first portion of the comparative signal, and

the second data electrical signal being generated from a light signal that includes light from the second portion of the reference signal and the second portion of the comparative signal.

16. The system ofclaim 15, wherein the local electronics are configured to perform a Complex Fourier transform on a complex signal, the first data electrical signals being a real component of the complex signal and the second data electrical signals being an imaginary component of the complex signal.

17. The system ofclaim 1, wherein the signal received from the LIDAR chip is one of multiple signals that the local electronics receive from the LIDAR chip,

the signals received from the LIDAR chip including a first data electrical signal and a second data electrical signal.

18. The system ofclaim 17, wherein the local electronics are configured to perform a Complex Fourier transform on a complex signal, the first data electrical signals being a real component of the complex signal and the second data electrical signals being an imaginary component of the complex signal.

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